1. Field of the Invention
The invention is directed to blood analysis instrumentation used to monitor force development or elastic modulus for a blood sample during clotting and dissolution.
2. Background Description
Blood analysis instrumentation used to analyze force development and elastic modulus of a blood sample during clotting and dissolution of a blood clot is described in detail in U.S. Pat. Nos. 4,986,964, 5,205,159, and 5,293,772 to Carr. The complete contents of these patents is herein incorporated by reference. As explained in the Carr patents, blood samples placed between a pair of spaced apart plates, one of which is connected to a transducer, can be evaluated for force development by measuring the pulling force caused by the blood clot. Force development is dependent on platelet function and arises from the internal actions of the platelets during clot retraction. Clot retraction is dependent on intact platelet membrane structure, normal platelet metabolic function, fibrin structure and normal platelet-fibrin interactions. Changes in clot retraction are sensitive to a spectrum of fluid phase and platelet abnormalities. If platelet function is abnormal or if platelets are absent, force development will be reduced or not occur. Measuring force development can be used in assessing risk of bleeding or thrombosis or a patient""s propensity for stroke or other disorders. Clot dissolution can be identified as a decrease in elastic modulus. This can occur with the addition of dissolving agents such as tissue plasminogen activator (t-PA). Monitoring the effects of such dissolving agents on blood clots can assist in assessing the fibrinolytic potential of whole blood. Determination of elastic modulus assists physicians in assessing clot structure and is a measure of erythrocyte flexibility and general clot structure. As described in U.S. Pat. Nos. 5,205,159 and 5,293,772, by periodically applying a known amount of force to an upper plate, and by determining the deformation of the clot during clotting, the elastic modulus can be calculated.
It is an object of this invention to provide a disposable cone and cup for use in blood analysis instrumentation used to assess platelet function and clot structure. The disposable nature of the cone and cup provides benefits of safety and productivity because the clinicians are not required to clean patient blood samples from reusable plates.
It is another object of this invention to provide an automated calibration check method for use with blood analysis instrumentation used to assess platelet function and clot structure. By using a top member, e.g., a disposable cone, that is of a known mass and which is selectively detachable from a holding means that holds the top member a slight distance above the receptacle, the displacement or downward gravitation force on a transducer can be measured. A measurable difference will result when the top member is attached and when it is unattached. If this difference is within a specified tolerance, then the instrumentation can be deemed to be within the calibration specifications required for proper operation of the instrumentation.
It is yet another object of the invention to provide on-board mixing capabilities and on-board reagent delivery in blood analysis instrumentation. Automation of the instrumentation is highly desirable. Mixing reagents directly in the receptacle can enhance automation of instrumentation designed for analysis of platelet function and/or clot structure. By providing a mechanism to rotate the top member relative to the receptacle, mixing within the receptacle can be achieved. A preferred mechanism may include a plurality of fins which are driven by an air source; however, direct drive mechanisms might also be used. By providing a mechanism to deliver reagent directly in the receptacle, the need for a separate preparatory operation is avoided. In a preferred embodiment, the reagent is carried within the body of the top member, and is combined with the blood sample while in the receptacle.
According to the invention, the cone and cup are used as the top and bottom plates of the blood analysis instrumentation, and force development between these two members is monitored and used to assess the platelet function and clot structure. The conical shape allows for easy alignment of the cone and cup, and provides greater surface area to interact with the blood sample. Preferably, the cone and cup are disposable, thereby enhancing instrument cleanliness as well as productivity and safety for the clinicians. For example, for each test to be performed, the cup, which will preferably be in the form of a thin plastic liner (e.g., high density polyethylene, polyvinyl chloride, etc.), is inserted into a receptacle, and the cone shaped top member is positioned within the confines of the receptacle, but spaced slightly above the receptacle surfaces such that blood can engage the surfaces of both the receptacle (i.e., at the liner) and the top member (i.e., at the conical end). During clotting, the top member will be pulled by clot retraction forces toward the receptacle, and this force development is measured using a transducer that is preferably connected to the top member. Clot elastic modulus may also be measured by periodically applying a compression force to the top member and calculating the modulus based on the applied force and the deformation of the clot.
Using a top member of a known mass that is detachable from the blood analysis instrumentation permits an automated calibration check to be performed simply by comparing displacement or force measurements with and without the top member attached. In addition, the top member can be modified to allow for mixing the blood sample with reagents, and for carrying reagents on board which may be used for clot retraction and clot dissolution analysis. Bar coding permits different top members to be identified in an automated fashion (e.g., top members carrying different reagents, and which may require different mixing operations).